Warming of aquatic ecosystems disrupts aquatic-terrestrial linkages in the tropics

Aquatic ecosystems are tightly linked to terrestrial ecosystems by
exchanges of resources, which influence species interactions, community
dynamics and functioning in both ecosystem types. However, our
understanding of how this coupling responds to climate warming is
restricted to temperate, boreal, and arctic regions, with limited
knowledge from tropical ecosystems. We investigated how warming aquatic
ecosystems impacts cross-ecosystem exchanges in the tropics, through the
export of aquatic resources into the terrestrial environment and the
breakdown of terrestrial resources within the aquatic environment. We
experimentally heated 50 naturally assembled aquatic communities,
contained within different sized tank-bromeliads, to a 23.5 - 32°C
gradient of mean water temperatures. The biomass, abundance, and richness
of aquatic insects emerging into the terrestrial environment all declined
with rising temperatures over a 45-day experiment. Structural equation and
linear mixed-effects modelling suggested that these impacts were driven by
deleterious effects of warming on insect development and survival, rather
than being mediated by aquatic predation, nutrient availability, or
reduced body size. Decomposition was primarily driven by microbial
activity. However, total decomposition by both microbes and
macroinvertebrates increased with temperature in all but the largest
ecosystems, where it decreased. Thus, warming decoupled aquatic and
terrestrial ecosystems, by reducing the flux of aquatic resources to
terrestrial ecosystems but variably enhancing or reducing terrestrial
resource breakdown in aquatic ecosystems. In contrast with increased
emergence observed in warmed temperate ecosystems, future climate change
is likely to reduce connectivity between tropical terrestrial and aquatic
habitats, potentially impacting consumers in both ecosystem types. As
tropical ectotherms live closer to their thermal tolerance limits compared
to temperate species, warming can disrupt cross-ecosystem dynamics in an
interconnected tropical landscape and should be considered when
investigating ecosystem-level consequences of climate change.